Author + information
- Received September 16, 2016
- Revision received September 30, 2016
- Accepted October 6, 2016
- Published online November 30, 2016.
- Christian A. Torres, MD,
- Marcelo E. Helguera, MD,
- Sergio L. Pinski, MD and
- Jose L. Baez-Escudero, MD∗ ()
- Section of Cardiac Pacing and Electrophysiology, Robert and Suzanne Tomsich Department of Cardiology, Cleveland Clinic Florida, Weston, Florida
- ↵∗Reprint requests and correspondence:
Dr. Jose L. Baez-Escudero, Section of Cardiac Pacing and Electrophysiology, Cleveland Clinic Florida, 2950 Cleveland Clinic Boulevard, Weston, Florida 33331.
- arrhythmogenic right ventricular cardiomyopathy
- inappropriate shocks
- subcutaneous defibrillator
A 41-year-old woman with arrhythmogenic right ventricular cardiomyopathy due to a plakophilin-2 mutation received a subcutaneous implantable cardioverter-defibrillator (S-ICD) for primary prevention at an outside hospital in 2013. The patient had adequately passed all the screening vectors during upright and supine postures. The device (S-ICD model number 1010 SQ-RX, Boston Scientific, Marlborough, Massachusetts) was implanted in the standard anatomic location without complications. It was programmed with conditional and shock zones of 200 and 250 beats/min, respectively. Sensing was optimally selected via the secondary vector. Defibrillation threshold testing was performed, and 2 consecutive defibrillations at 65 J were achieved successfully.
The patient subsequently presented with symptomatic monomorphic ventricular tachycardia (VT) below the cutoff rate (CL 400 ms) and underwent a VT ablation elsewhere (Epi/Endo) in 2014, which was unsuccessful. She had failed sotalol and was taking flecainide for prevention of VT recurrence.
One year later, she presented to our hospital with several sequential ICD shocks and syncope while dancing. Device interrogation (Figure 1A) showed inappropriate P (PWO) and T-wave oversensing (TWO) during sinus tachycardia. The initial inappropriate shock (IAS) was pro-arrhythmic and induced a monomorphic, hemodynamically significant VT that caused syncope. The VT was appropriately sensed and a second appropriate 80-J shock was delivered, which failed to rescue. A third 80-J shock terminated the VT and restored sinus tachycardia (Figure 1B); however, TWO and PWO persisted, and she received 2 additional IAS for sinus tachycardia shortly after.
Because in the S-ICD both the sensing algorithm and the discrimination algorithm are fixed and can only be modified indirectly by changing the frequency of the therapy zones or the stored template, we attempted to circumvent the oversensing noninvasively. First, a conditional zone between 170 and 220 beats/min and an unconditional zone between 220 and 250 beats/min were programmed. She then underwent an exercise test to optimize sensing. All vectors were evaluated first without changing the template, without success. Unfortunately, despite making a new template during maximal exercise, both PWO and TWO persisted in all 3 sensing vectors. The SMART Pass Filter option was not available in this older S-ICD model. Because there were no further noninvasive options to optimize the device, we opted next for a lead revision, after rescreening her satisfactorily with surface electrodes. The lead was extracted and a new S-ICD lead was subsequently reimplanted in a more medial parasternal subcutaneous location. The sensing vector was changed after performing a complete automatic setup. Defibrillation threshold testing was appropriate again at 65 J. Unfortunately, the patient returned 3 weeks later with more IAS due to oversensing of myopotentials and TWO. Because the recurrent risk of IAS remained significant, we elected to remove the S-ICD and replace it with a transvenous ICD. The fact that an 80-J shock was pro-arrhythmic once (i.e., below the upper limit of vulnerability) indicated a lack of safety margin between the energy required for defibrillation and the maximum output of the device. Also, her clinical VT was slow (CL 400 ms, below the S-ICD cutoff rate) and had been effectively pace terminated during electrophysiology study/VT ablation. Painless antitachycardia pacing delivered via a transvenous ICD was deemed more useful in this particular case. Our decision was based on the inability to solve the sensing issues, the desirability to provide antitachycardia pacing, and the lack of safety margin with the subcutaneous system.
This case highlights the potentially dangerous pro-arrhythmic effect of IAS with the S-ICD as well as the potential changes in defibrillation threshold testing over time. Patients with arrhythmogenic right ventricular cardiomyopathy are often deemed reasonable candidates for S-ICD due to the relative young age at diagnosis and usual lack of pacing indications. Careful selection of device options for this population remains challenging.
Drs. Pinski and Baez-Escudero are consultants for St. Jude Medical. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.
- Received September 16, 2016.
- Revision received September 30, 2016.
- Accepted October 6, 2016.
- American College of Cardiology Foundation